Processing of pineapple juice



Patented Jan. 31, 1950 PROCESSING OF PINEAPPLE JUICE George M. Eguchi and Clinton H. Wells, Honolulu, Territory of Hawaii, assignors to Hawaiian Pineapple Company, Limited, Honolulu, Territory of Hawaii, a corporation of Hawaii Application September 4, 1948, Serial No. 47,784

6 Claims.

This invention relates to the processing of pineapple juice and more particularly pertains to the separation of albumin, fruit oils and waxes from raw pineapple juice as obtained, for example, from the waste resulting on the preparation of cylinders of pineapple for slicing and canning.

Such juice contains substantial amounts of pulp and must be subjected to filtering and screening operations before it is processed for the recovery of liquid sugars, citric acid and clarified syrups. These operations are quite time-consuming due chiefly to the formation of coagulates in the juice which tend to clog the filter media.

We have discovered that the coagulates are constituted of particles of coagulated albumin and particles of oil and wax coated with coagulateol albumin and we have further discovered that there is contained in raw pineapple juice a natural frothing agent, the chemical nature of which we have been unable to ascertain, which renders it possible to effect separation of the coagulates by a flotation procedure.

The efiectiveness of our procedure is due, not alone to the presence of the frothing agent, but also to the aflinity of coagulated albumin for gas bubbles. Apparently, we are the first to recognize this aflinity, for, although albumin has been employed heretofore in the separation of minerals by flotation, it has always been used in the uncoagulated state as a dispersing agent to avoid collection of certain unwanted minerals in the froth rather than as a collecting agent.

Our flotation procedure is characterized in that the juice is maintained at a temperature between the coagulating temperature of albumin and the boiling point of the juice and in that the necessary gas bubbles are introduced well below the surface of the juice with controlled agitation. The albumin, oil and wax are separated as a froth from the surface of the juice. Depending on operating factors, a major portion of the pulp may also be removed in the froth. Thus, in one typical run, the content of suspended pulp was reduced from 6.0% to less than 2.0% on a volumetric basis as determined by a centrifuge test.

Generally, we find it advantageous to maintain the juice during the flotation at a temperature within the upper half of the range previously indicated, e. g., 190 F.-200 F. Such a temperature promotes the spreading of the waxes, some of which are solid or semi-solid at lower temperatures; accelerates the coagulation of the albumin and the coating of the oil, waxes and pulp particles with coagulated albumin; maintains the juice at a viscosity reducing loss of juice in the froth; provides more fragile and consequently more easily ruptured bubbles at the liquid surface, a condition favoring production of a froth richer in the substances it is desired to separate; and otherwise beneficially affects the course of the flotation.

We have found it preferable, particularly when we wish to remove substantial amounts of pulp, to subject the raw juice to a preliminary screening operation to clear it of solids coarser than about 30 mesh. The flotation can be, and preferably is, carried out in a continuous manner, for example, by passing the juice through a series of connected flotation cells of a capacity providing an adequate total retention period. No special equipment is required, whether the process is practiced in a batchwise or continuous manner, standard flotation cells of the subaeration type as employed, for example, in minerals separation being, for the most part, suitable. We have found it advantageous as shortening the time required to effect the substantially complete removal of the albumin, oil and wax to raise the pH of the juice to about 3.94.2, using lime as the reagent. In no case should the amount of lime used be such as to cause the precipitation of citrates. We have been unable to determine why the slight increase in pH operates to reduce the time required for the separation, but it appears to increase the fragility of the froth and consequently to render it more free draining. Normally, we do not add extraneous albumin, but this may be necessary at times due to seasonal variations in the constituents of the juice. In lieu of albumin, substances functionally equivalent may be employed, casein or milk solids, for instance.

Our invention will be better understood from the accompanying drawings illustrating schematically a system of apparatus suitable for its practice. In the drawings, Fig. 1 is a sectional elevation, Fig. 2 is a transverse section,

The apparatus will be seen as comprising a feed box Ill into which the juice is introduced via a conduit H. The feed box opens into the first of a series of connected cells [2, the last of which communicates with a discharge box M from which the partially clarified juice is withdrawn via a discharge pipe l5. Interposed between the cells and between the end cells and the boxes with which they communicate are adjustable baflles i6 allowing continuous flow of juice toward the discharge end, but retaining a predetermined level of froth in each cell. Juice entering box Ml flows over a weir IT by means of which the flow may be gauged. On either side of each cell is an adjust- 3 able froth overflow lip, discharging through chutes It to pipes I.

Agitation and aeration of the Juice may be effected by any suitable means, it being necessary, however, that the agitation be confined to a zone directly around the agitator and that swirling or surging at the surface of the juice be held to a minimum. Also, it is important that the gas bubbles be introduced well below the surface of the liquid. In the drawings, agitation and aeration of the juice is shown as effected by a rotary type agitator comprising a stator 20 and a rotor II, the rotor shaft 22 being powered by a motor 23, the power transmission being by belt and pulley. Mounted above the stator and rotor is an annular shield 24 opening to the atmosphere.

In operation, air drawn into the agitator is broken down into fine bubbles which become partially dissolved in the juice in the pressure area ahead of the rotor blades and which are precipitated as minute bubbles charged with water vapor in the area of partial vacuum behind these blades.

In order to maintain the juice at proper temperature during flotation, heating coils 25 are provided. Normally, the juice is preheated prior to being charged to the apparatus and is also screened, as has been indicated, to remove solids coarser than 30 mesh.

The froth overflowing from the first two cells is heavily loaded and is yellow with pineapple oil. It condenses to a thick slurry which is practically unfllterable. During the collection of this yellow froth, the fiow of air to the rotor stator unit should be unrestricted. The color of the froth during the last half of the operation changes to white, and gray clots of fibrous pulp appear at the bubble film intersections. This is accompanied by an increase in the froth level and may necessitate restriction of the air intake of the agitator unit in order to prevent excessive overflow. The white froth is more fragile and breaks down soon after overflow to a thick slurry of pulp. Soil particles may be noticed in the froth overflowing the last cell.

The rate of flow of the juice is, of course, determined by the degree of separation sought and depends, too, on the size of the equipment and operating conditions. Although the pH adjusting agent, assuming such an agent is used, may be added to the juice in the cells, we ordinarily effect the pH adjustment before charging the Juice to the cells. Also, any necessary extraneous albumin or other collecting agent is ordinarily added to the juice before the same is worked.

The improvement provided by our invention in the respect of the filtering characteristics of the eiiluent juice is of a high magnitude. Thus, the eflluent juice from the run referred to hereinbefore having a total solids content of less than 2.0% as compared with 6.0% in the case of the" juice before treatment showed a gravity filtration rate 100-130 times that of the original juice.

Our invention may, of course, be practiced using nitrogen or other gas in lieu of air. Some bubble precipitation, of course, results from heat displacement of gas dissolved in the cold juice, and these bubbles supplement the action of those produced by the agitating mechanism.

It is to be emphasized that our process does not depend on the formation of a bulky flocculent precipitate capable of suspending solids or upon maintaining conditions favoring agglomeration of such a precipitate to a size which will permit rising gas bubbles to mechanically lift the solids to the surface; rather our invention is dependent on the gas adhesive properties of albumin which allow for true bubble attachment.

We claim:

1. Method of treating a raw pineapple juice which comprises introducing minute gas bubbles into a body of the juice, maintained at a temperature above the coagulating temperature of albumin but below the boiling temperature of the juice. at a point below the surface of the body while agitating the body, the agitation being confined substantially to the area of gas introduction, and recovering a froth concentrate of albumin, fruit oil and waxes from the surface of the body.

2. Method of treating a raw pineapple juice which comprises introducing minute air bubbles into a body of the juice, maintained at a temperature between F. and 200 F., at a point below the surface of the body while agitating the body, the agitation being confined substantially to the area of air introduction, and recovering a froth concentrate of albumin, fruit oil and waxes from the surface of the body.

3. Method according to claim 2, further characterized in that extraneous albumin is added to the juice.

4. Method according to claim 2, further characterized in that an extraneous collection agent from the group consisting of albumin, casein and milk solids is added to the juice.

5. Method of treating a raw pineapple juice which comprises introducing minute air bubbles into a body of the juice, maintained at a temperature between 190 F. and 200 F. and at a pH of from 3.9 to 4.2, at a point below the surface of the body while agitating the body, the agitation being confined substantially to the area of air introduction, and recovering a froth concentrate of albumin, fruit oil and waxes from the surface of the body.

6. Method according to claim 5 where the desired pH is maintained with lime.

GEORGE M. EGUCHI. CLINTON H. WELLS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,527,304 Heyman Feb. 24, 1925 1,940,013 Peterson Dec. 19, 1933 1,994,670 Scott Mar. 19, 1935 2,104,415 Davies Jan. 4, 1938 OTHER REFERENCES Chemical Engineers Handbook 2nd edition, pages 1736-1737, McGraw-Hill Book C0,, New York, 1941. 

1. METHOD OF TREATING A RAW PINEAPPLE JUICE WHICH COMPRISES INTRODUCING MINUTE GAS BUBBLES INTO A BODY OF THE JUICE, MAINTAINED AT A TEMPERATURE ABOVE THE COAGRULATING TEMPERATURE OF ALBUMIN BUT BELOW THE BOILING TEMPERATURE OF THE JUICE, AT A POINT BELOW THE SURFACE OF THE BODY WHILE AGITATING THE BODY, THE AGITATION BEING CONFINED SUBSTANTIALLY TO THE AREA OF GAS INTRODUCTION, AND RECOVERING A FROTH CONCENTRATE OF ALBUMIN, FRUIT OIL AND WAXES FROM THE SURFACE OF THE BODY. 